1. Field of the Invention
This invention pertains to an apparatus for releasing potentially damaging pressure which may occur within a pipeline and more particularly to an apparatus for releasing the pressure resulting from water hammers before such pressure can cause damage to a pump or the like connected to the pipeline.
2. General Background
In long pipeline systems where one or more booster pumps are needed to deliver fluid across great distances, water hammers will occur. A water hammer is a change in pressure within the pipeline, either above or below the normal pressure, caused by a variation of the flow rate in the pipeline. Every time the flow rate is changed, either increased or decreased, a water hammer is developed. Normally, in small diameter pipes with low flows, the stresses created are not critical. However, in larger pipelines with relatively high flow rates, the stresses created can be significant enough to damage downstream equipment, including booster pumps.
Water hammers are a function of the momentum of the fluid in the pipeline, such momentum being equal to the mass of the fluid times its velocity. Whenever a change in this momentum occurs, such as by closing a valve or otherwise altering the flow rate of the fluid, such a change will cause pressure to build-up which is transmitted along the pipe. In some cases, this pressure will rise until it is large enough to overcome the momentum of the fluid thereby bringing the fluid in the pipe to a standstill, thus initiating a water hammer. At the instant such a pressure wave reaches a reservoir or the like, the fluid in the pipe is motionless but at a pressure much higher than normal. Consequently, this difference in pressure between the pipe and the reservoir will cause the fluid in the pipe to rush into the reservoir thereby reducing the pressure within the pipe. However, at the time the pressure within the pipe reaches normal levels, the fluid has attained considerable momentum out of the pipe. Thus, a negative pressure is created within the pipe which will eventually cause the fluid to stop flowing into the reservoir and reverse its direction back into the pipe. As the fluid flows back into the pipe, pressure within the pipe increases to above normal levels thereby creating significant forces that, if not diffused, may damage surrounding equipment. This cycle of high and low pressure build-up will normally continue to occur until friction dampens these oscillations or until such pressure is released by a rupture of the pipe or the like. Because of the high velocity of the pressure waves involved, each cycle may take only a fraction of a second to occur.
Usually, it is uneconomical to design long pipelines to withstand the pressures that are created by water hammers. Additionally, it is oftentimes not economical to operate valves slowly enough such that a water hammer is not created in the first place. To thus compensate for the water hammers that are created in long pipelines, a surge tank is oftentimes coupled to the pipeline close to valves at the end of the pipeline. Consequently, when a valve is suddenly operated, the water in the pipe will flow either into or out of the surge tank thereby dampening any pressure build-up that may occur. Unfortunately, however, for the surge tank to operate effectively, it generally must be open to atmospheric pressure, thus the pipeline can only be pressurized up to the amount of head provided by the surge tank. Additionally, installing multiple surge tanks in long runs will significantly increase the cost of the pipeline. A typical surge tank system is shown by U.S. Pat. No. 4,652,222 to Aiba.
Other potential solutions to the water hammer problem are shown by U.S. Pat. No. 1,776,937 to Timbs, et al. and U.S. Pat. No. 2,752,754 to Jaseph. Unfortunately, these devices provide only a fixed volume into which the pressure can be released, thus in large diameter pipelines, should more volume be needed to relieve the pressure, these devices will not be sufficient.
In pneumatic systems, typical pressure relief systems are shown by U.S. Pat. No. 1,952,916 to Etten and U.S. Pat. No. 4,177,023 to Kamiya, et al. These devices, by pertaining to pneumatic systems, are not suitable for liquids flowing through the pipeline because such liquids may cause blockage or otherwise interfere with the seals in these devices. These inventions also suffer as a result of the limited volume provided for relief purposes.
It is thus an object of this invention to provide an apparatus for relieving the pressure that may occur due to water hammers. Another object of this invention is to provide an unlimited volume into which such pressure can be released thereby avoiding the restrictions imposed upon previously known devices. Still another object of this invention is to provide an apparatus that can be adapted to both small and large diameter pipelines. Yet another object of this invention is to provide pressure relief which can be adjusted, as needed, to accommodate the various equipment that may be installed or will be installed along the pipeline. Still another object of this invention is to provide pressure relief without the need for surge tanks such that the pipeline may be pressurized for greater flow therethrough. A further object of this invention is to provide such pressure relief at low cost and with an apparatus that require little maintenance. These and other objects of this invention will become obvious upon further investigation.